a. Field of the Invention
The present invention relates to a novel method of preparing liquid olefin polymers.
B. Description of the Prior Art
As a method for polymerization of olefins, the cationic polymerization method employing the Lewis acids such as aluminum chloride has been known for a long time. According to this method, however, the degree of polymerization becomes so high under the ordinary reaction conditions that there can be obtained only high molecular-weight liquid polymers. It is of course possible to obtain low molecular-weight polymers subject to elevating the temperature for polymerization, but in this case, there are generated great quantities of dimers of olefin as byproduct, which are disqualified for use as a lubricant or a cosmetic base. Also, the catalyst system of this method has the drawback that it is apt to give rise to the skeltal isomerization of olefins and renders only such liquid polymers as having a low viscosity index and being unsuitable for use as a lubricant.
There has been proposed a Japanese patent publication No. 3804/1969 a method of effecting polymerization of olefins in the presence of a liquid catalyst prepared by dissolving excess aluminum halide in a complex consisting of aluminum halide and ethyl acetate at the molar ratio of 1:1. However, inasmuch as said complex does not act as a catalyst, the effect of this method is no more than cationic polymerization employing the aluminum halide added in excess. Therefore, even by this method employing a complex, there can be obtained only a high molecular-weight polymer under the ordinary polymerization conditions, and it is infeasible to obtain liquid polymers having various mean molecular weights.
Nowadays, from the view point of overcoming these drawbacks in the prior art, the use of the so-called Ziegler catalyst consisting of an organic aluminum and titanium tetrachloride as a catalyst for polymerization of olefins has come into the limelight. The use of this catalyst alters the atomic ratio of aluminum to titanium, and the higher is said atomic ratio altered thereby, the higher becomes the molecular weight of the resulting polymers, whereas the lower is said atomic ratio, the lower becomes the molecular weight of the resulting polymers. That is, by altering this atomic ratio, it is possible to obtain polymers having various mean molecular weights.
As a matter of fact, however, just a minor alteration of the atomic ratio would bring on a remarkable alteration of the mean molecular weight of the resulting polymer and it is difficult to obtain liquid polymers having various mean molecular weights. Besides, this method is poor in reproducibility and is low in yield, so that it is unsuitable for practical use.